Integrating conveyor scale

ABSTRACT

An improved method and apparatus for measuring the rate at which material is transferred through a region and for measuring the total quantity of material transferred through the region over a period of time. A pulse train is generated having constant width pulses which are repeated at a rate proportional to the speed at which the material is transferred through the region. The pulse train is amplitude modulated with an analog signal which is proportional to the instantaneous weight of material in the region. The modulated pulse train is then filtered or averaged to obtain a continuous analog signal which is proportional to the transfer rate for driving a rate indicating meter. The rate signal is also converted to a frequency modulated pulse signal for stepping a counter which indicates the total quantity of material transferred over a period of time. Circuitry is provided for automatically zeroing the analog weight signal and for inhibiting measurements of less than a predetermined percentage of the maximum capacity of the apparatus.

United States Patent 1191 Williams, Jr.-

[ Aug. 21, 1973 INTEGRATING CONVEYOR SCALE Primary Examiner-Joseph F.Ruggiero [75] inventor: Roger B. Williams, Jr., Sylvania,Attorney-Thomas Gram) Ohio [73] Assignee: Reliance Electric Company,Toledo, [57] ABSTRACT ()hi An improved method and apparatus formeasuring the rate at which material is transferred through a region[22] Ffled: 1972 and for measuring the total quantity of material trans-21 215,370 ferred through the region over a period of time. A pulse 7train is generated having constant width pulses which are repeated at arate proportional to the speed at [52] Cl 23815133 177/ 235/ which thematerial is transferred through the region. 235/183 The pulse train isamplitude modulated with an analog [5 l Int. Cl. G018 1 1/14, G068 7/18signal which i proportional to the instantaneous weight [58] Field ofslfch 235/.l94, 183, 151.33, of material in the region. The modulatedpulse rain is 235/15052, 150.51 150.5, 177/3, 4, 1 then filtered oraveraged to obtain a continuous analog 25 198/39 l l; 214/2 signal whichis proportional to the transfer rate for driving a rate indicatingmeter. The rate signal is also con- [56] Reference Cmd verted to afrequency modulated pulse signal for step- UN TED S S PATENTS ping acounter which indicates the total quantity of ma- 3,6l0,908 10/197!Karosas 177/16 X terial transferred over a period of time. Circuitry ispro- 3,358,l29 l2/l967 Schultz 235/194 vided for automatically zeroingthe analog weight sig- 3.333.649 8/1967 Schflfstellerw 177/16 X nal andfor inhibiting measurements of less than a pre- 1 1 9/1969 Connolly 235/194 X determined percentage of the maximum capacity of the 3,500,2003/1970 Woodhead..... 235/194 X apparatus. 3,662,845 5/1972 Pratt 177/2517 Claims, 8 Drawing Figures I u m rnnmspeq I "213571046 RATE I ME TERMsTsR 4 I Dawn, FIG. 3. I L u ew I in I A I 7 LOADCELL AUWMITIC I uLnPuiyn/5mg VOLTAGE my"!!! mo'roa- Home LOETIAGLT S A P 511mm. :3; claculrcmcwr l Ja Egg MOTOR .ecouursg I PREAMP- SIGNAL CQNVERTE'I REVERSE 1tONDlTIIlNlNG I I 4 J z z 1 L L l M g 2 L. E w .5 L z. .....2 21x .2 o

FlG.S. i GATEDQ nuromnc I CONSTMT CLOCK i rowan zsno WIDTH PULSE 1 iSUPPLY TIMING PULSE sruraaror 1K 70 I I GENERATOR M /5 m. 5 .3 mi 5 ITMHOMETER mamuzma AM'LH'IER CIRCUIT i AND SIGNM. (mvloro BY l, n 1;rncnomrra counlrlours z,4,s,|s,o11az) i Patented Au 21, 1973 3,154,126

6 Sheets-Sheet 73 GATED POWER T 99 i5 SUPPLY 99 w 3 p 47 Zfz- @132 ONESHOT TIMING CIRCUIT ITS-3" I NORMALIZER P T 4--BIT a BINARY COUNTER I #557 55 1 2 2 H; 62

(i smmw r 'CouNTER Q. I15 Z Patented Au 21, 1973 3,754,126

6 Sheets-Sheet LS Patented Aug. 21, 1973 I 3,754,126

6 Sheets-Sheet 4 ANALOG wbusm SIGNAL on 87 SPE ED PULSE SPEED-WEIGHT IPaooucT-Ar- 1 AMPLIFIER us I I I I I I V to t. n

TIE-4E Patented Aug. 21, 1973 6 Sheets-Sheet 6 A. TIMING PULSE FROM /0285 (ILOSED c. GATED OFF vows. SUPPLY ON D.AuT0- OPEN ZERO swn'cu CLOSE z4s'i Ms-Ec.

VOLTAGE 0N \5'7 VOLTAGE 0N I57 CLOCK LINE 6| 1 INTEGRATING CONVEYORSCALE BACKGROUND OF THE INVENTION This invention relates generally tomeasuring apparatus, and more particularly to an improved-integratingconveyor scale and method for totalizing the quantity of materialtransported through a region on conveying apparatus such as a beltconveyor and for simu'lta neously measuring the instantaneous rate atwhich the material is transferred through the region.

In bulk material handling, it is often desirable to measure the totalquantity of material delivered or transferred over a period of time andto measure the rate at which material is being transferred at any giveninstance. Bulk materials are often transferred, for exam ple, from asupply hopper into a batch hopper by means of either a belt conveyor orof a screw conveyor. When batch ingredients are compounded within abatch hopper according to a formula, a measure of the total weight ofeach ingredient delivered into the batch hopper is quite important tomaintain the compounded batch within predetermined tolerance limits forthe formula. Such measurements may be made by conveyor scales.

It is readily apparent that the product of the speed at which materialis delivered through a region times the weight of material within theregion will equal the delivery rate. For example,- if five pounds ofmaterial are on a one lineal foot segment of a belt conveyor moving atten feet per minute, the instantaneous transfer rate for this segment ofthe conveyor is 50 pounds per min= ute. If this transfer rate is shownas a curve on a graph with respect to time, it will be appreciated thatthe area under the curve over a time interval, or the integral ofgrating scales have also at times been inefficient. Difficulty inchanging the range of a scale to meet requirements of each installationhas resulted in the use of less than an optimum range in manyinstallations. When, for example, a tachometer has been used to measurethe speed of a conveyor, it has been necessary to change drive gears forthe tachometer to bring the scale output within a suitable range.Problems have also occurred during installation of prior art integratingconveyor scales due to the bulkines's and mechanical limitations of suchscales and the need to meet limited available space at someinstallations.

' SUMMARY OF THE INVENTION According to the present invention, animproved integrating conveyor scale and an improved measuring method areprovided for accurately measuring the rate at which a material istransferred and for simultaneously measuring the total weight ofmaterial transferred over a period of time. The scale includes atachometer or similar apparatus for generating an alternating currenthaving a frequency proportional to the speed at which the material istransferred. The output of the tachometer is amplified, conditioned andconverted into a pulse train having constant width pulses which arespaced or repeated at a rate proportional to the speed at which thematerial is transferred. Circuitry is provided for electronicallynormalizing or selectively dividing the pulse train by any of severalpredetermined values to establish a range for the scale suitable fordifferent conveyor speeds in different installations without the need ofchanging drive gears for the tachometer.

The scale also includes one or more load cells for generating an analogsignal proportional to the weight of material in a region through whichthe material is conveyed. The analog weight signal is periodically interrupted and the weighing apparatus is automatically zeroed tocompensatefor zero drift and transient signals. A constant output signalis maintained while the load cell output is interrupted for the zeroingoperation.

A multiplier or modulator circuit modulates the amplitude of theconstant width pulses from the conveyor speed measuring circuitry inresponse to the analog weight signal. The resulting signal is thenaveraged to obtain a continuous analog signal proportional to theinstantaneous rate at which the material is transferred. This signal maybe amplified to drive an instantaneous transfer rate indicating meterand to drive auxiliary equipment such as conveyor speed controlequipment. The transfer rate signal is also converted in avoltageto-frequency converter to obtain a pulse signal for stepping acounter. The counter measures and indicates the total'weight of materialtransferred over a period of time. The voltage-to-frequency converterand the counter thus integrate the analog transfer rate signal.

Accordingly, it is a preferred object of the invention to provideimproved apparatus for measuring the rate at which material istransferred and the total weight of material transferred over a periodof time.

Another object of the invention is to provide an improved integratingconveyor scale.

A further object of the invention is to provide an improved integratingconveyor scale including circuitry for automatically zeroing the scaleoutput for transient signals and zero drift occuring in the weightmeasuring portion of the circuitry. 1

, Another object of the invention is to provide an improved method and,circuitry for changing the range of an integrating conveyor scale tomeet specific installation requirements for such scale.

Still another object of the invention is to provide an improved methodand improved circuitry in a conveyor scale for multiplying conveyorspeed times the instantaneous weight of material being conveyed througha region to measure the instantaneous transfer rate.

Other objects and advantages of the invention will become apparent fromthe following detailed description, with reference being made to theaccompanying drawings. 5

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of animproved integrating conveyor scale constructed in accordance with thepresent invention;

FIG. 2 is a detailed schematic logic diagram of 'a circuit forgenerating a frequency modulated pulse train having constant widthpulses which: are repeated at a rate proportional to the conveyor speedin an integrating conveyor scale according to the present invention;

FIG. 3 is a detailed schematic logic diagram of cir cuitry forgenerating an analog signal proportional to the weight of material on aconveyor segment and of the automatic zero circuitry in an integratingconveyor scale according to the present invention;

FIG. 4 is a detailed schematic logic diagram of the multiplier ormodulator circuitry, the averaging circuit and the rate indicatingcircuitry in an integrating scale constructed in accordance with thepresent invention;

FIG. 4a is a graph showing the operation of the multiplier circuitry ofFIG. 4;

FIG. 5 is a detailed schematic logic diagram of voltage-to-frequencyconverter and of a counter circuit for indicating the total weight ofmaterial conveyed over a period of time for an integrating conveyorscale according to the present invention;

FIG. 6 is a graph showing the timing of the automatic zero circuitry ofFIG. 3; and

FIG. 7 is a graph showing operation of the voltage-tofrequency converterof FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a blockdiagram is shown of an improved integrating conveyor scale 10constructed in accordance with the present invention. The scale 10 isparticularly suitable for measuring the rate at which material istransferred on, for example, a belt conveyor and for measuring the totalweight of material transferred over a period of time. It will,of course,be appreciated that the scale 10 is adaptable for use with other typesof conveyors such as screw conveyors and pipes or conduits conveyingeither a fluid or a particulate material. In the following description,the scale 10 is described in combination with a belt-type conveyor.However, the scale 10 is clearly not limited to use with only beltconveyors.

A conventional tachometer 11 is driven by the belt conveyor forgenerating either a pulse signal or an alternating current having afrequency proportional to the speed of the conveyor. A circuit 12amplifies the output of the tachometer 11 and from such amplified outputgenerates a pulse train having the same frequency as the output of thetachometer 11. The pulse train from the amplifier and conditionercircuitry 12 passes through a normalizing circuit 13. The normalizingcircuit 13 selectively divides the pulse train by a factor of one, two,four, eight, 16 or 32 for electronically changing the range of theoutput of the scale 10. The normalizing circuit 13 facilitates use ofthe scale 10 with different belt conveyors having maximum speeds, forexample, of from 20 to 1,000 feet perr ninute.

The normalized pulse train is applied to a constant width pulsegenerator 14 which generates-a new train of pulses. Each pulse from thenormalizing circuit 13 initiates the formation of a new pulse at theoutput of the generator 14. The width of the output pulse from thegenerator 14 is fixed and is determined by a predetermined count oftiming pulses from a clock pulse generator 15. The output of theconstant width pulse generator 14 is applied to one input of amultiplier circuit 16.

The scale 10 generates a second signal from the belt conveyor. Thissignal is proportional to the weight of material on a segment of theconveyor or, in other words, the weight of material conveyed through apredetermined region. The region may, for example, com- I prise aportion of the conveyor belt extending between a pair of load carryingidlers which support a segment of the conveyor belt. The idlers aremounted on a frame which rests on one or more load cells 17. The loadcell 17, when energized by a gated power supply 18, generates an analogsignal which is proportional to the total weight on the load cell 17.The analog signal from the load cell 17 is applied through apreamplifier 19 to zeroing and conditioning circuitry 20. A timingcircuit 21 periodically turns off the power supply 18 to interrupt powerto the load cell 17. While power is interrupted, the timing circuit 21causes the conditioning circuit 20 to automatically establish a zerooutput, thus neutralizing or balancing the output of the preamplifier 19for transient signals and unbalanced conditions occurring, for example,from component ageing and temperature drift. While the timing circuit 21interrupts the output of the power supply 18, a signal is maintained atthe output of the conditioning circuit 20 which is identical to itsoutput immediately prior to interruption of the output of the powersupply 18. The output from the conditioning circuit 20 may also bebalanced or zeroed for the tare'weight of the conveyor belt and idlerson the load cell 17 such that the conditioning circuit 20 will have azero output when the conveyor belt is empty. The output of theconditioning circuit 20 is applied to the multiplier circuit 16.

The multiplier circuit 16 modulates the amplitude of the pulse trainfrom the constant width pulse generator 14 with the continuous analogweight signal from the conditioning circuit 20. The modulated pulsetrain output from the circuit 16 is, in effect, the product of the pulsetrain output of the generator 14 and the analog signal output from theconditioning circuit 20. The average value ofthe modulated pulse trainoutput from the multiplier circuit 16 is proportional to the rate atwhich material is conveyed on the belt conveyor. A circuit 22 averagesor filters the modulated pulse train to produce a continuous analogsignal which is proportional to the material transfer rate. This signalmay be amplified and dampened in a circuit 23 for driving aninstantaneous transfer rate meter 24. The amplified and dampened signalmay also be used for driving apparatus external to the scale 10, forexample, for driving a recorder or for driving control apparatus for theconveyor.

The continuous analog output from the averaging circuit 22 is alsoapplied to a voltage-to-frequency converter 25. Operation of theconverter 25 is controlled by timing pulses from the generator 15. Theconverter 25 generates a frequency modulated-pulse train which has afrequency proportional to the transfer rate. This pulse train is appliedthrough motor drive logic 26 for driving a stepping motor 27 forward orbackward, de-

pending upon the polarity of the analog output of the averaging circuit22. The stepping motor 27 drives a counter 28 which is calibrated toindicate the total weight of material conveyed by the belt conveyor overa period of time. The motor 27 is adapted to be driven eithel forward orin reverse so that the scale 10 may be set to an accurate dynamic zero.

In a preferred form, the voltage-to-frequency converter 25 is adapted tohave an inhibited or blocked output when the analog rate signal from theaveraging circuit 22 is less than a predetermined small percentage ofthe maximum transfer rate of the conveyor. The

voltage-to-frequency converter 25 may, for example, be adapted to haveno output when less than two percent of the maximum material transferrate is measured by the load cell 17 and the tachometer 11. Thisprevents the counter 28 from falsely indicating transient signalsoccurring when the belt conveyor is empty. The counter 28 also would notmeasure irregularities in the weight of the moving conveyor belt whenthe conveyor belt is empty.

Turning now to FIG. 2, a detailed schematic logic diagram is shown ofthe circuit for generating a pulse train having constant width pulseswhich are repeated at a frequency proportional to the speed of the beltconveyor. The tachometer 11 is driven at a speed and proportional to thespeed of the belt conveyor and may be of conventional design, such as amagnetic pulse generator or an alternating current generator. Thetachometer l 1 may be driven by any suitable means connected to the beltconveyor. The tachometer 11 may have either a pulse output or asinusoidal output which increases in frequency with increases in speedof the conveyor.

The output from the tachometer 11 is applied through a resistor 33 tothe input of an operational amplifier 34. A pair of reverse biaseddiodes 35 and 36 are connected in parallel between the input of theamplifier 34 and ground to clip or limit the maximum magnitude of theinput to the amplifier 34. A capacitor 37 is con nected between theoutput and the input of the amplifier 34, causing the amplifier 34 tointegrate its input. The output of the amplifier 34 will be determinedby the charge on the capacitor 37. This output has the same frequency asthe frequency of the alternating current output from the tachometer 11.

The output of the amplifier 34 is applied through a resistor 38 to apair of inverters 39 wired as a Schmitt trigger. A resistor 40 isconnected between the output and the input of the Schmitt trigger 39 fordetermining, along with the resistor 38, the hysteresis of the Schmitttrigger 39. The output of the Schmitt trigger 39, which is a directcurrent pulse train, is connected to a divideby-one terminal 41 on anormalizer jumper panel 42 and to the trigger input of a four-bit binarycounter 43. The binary counter 43 has four outputs which are connected,respectively, to a divide-by-two terminal 44, a

. divide-by-four terminal 45, a divide-by-eight terminal 46 and adivide-by-l6 terminal 47, all in the normalizer jumper panel 42. Thedivide-by-l6 output of the counter 43 which is attached to the terminal47 is also attached to the trigger input of a flipflop 48. The Q outputof the flip-flop 48 is connected to a divide-by-32 terminal 49 in thejumper panel 42. It will be readily apparent that the terminal 41 willhave a pulse for every pulse appearing at the output of the Schmitttrigger 39. The signal on the terminal 44 will change logic levels oncefor every pulse applied by the Schmitt trigger 39 to the trigger inputof the counter 43, thereby dividing the frequency of the output of theSchmitt trigger 39 by two. Similarly, the signal on the terminal 45 willchange for every two trigger pulses applied to the counter 43, thesignal on the terminal 46 will change for every four trigger pulses andthe signal on the terminal 47 will change for every eight triggerpulses. The flip-flop 48 is, in effect, a divide-by-two circuit whichcauses the signal on the terminal 49 to change for every sixteen triggerpulses from the Schmitt trigger 39. A common output terminal 50 from thejumper panel 42 is selectively connected by means of a jumper wire 51 toone of the terminals 41, 44, 45, 46, 47 or 49. The jumper wire 51 isshown in FIG. 2, for example, connected between the common outputterminal 50 and the divideby-two terminal 44. Thus, the output on theterminal 50 will change signs or logic levels once for every cycle orpulse of the output of the tachometer ll Each pulse appearing on theoutput 50 from the normalizer jumper panel 42 triggers a flip-flop 52 toset the Q output high and 6 output low. The high Q output from theflip-flop 52 is applied to the J input of a flipflop 53. The nexttrigger pulse applied to the flip-flop 53 sets the flipflop 53 to a high0 output and to a low 6 output 54.

A conventional crystal oscillator controlled clock 55 generates auniform pulse train for triggering a four-bit binary counter 56. The twooutput of the counter 56, which is one-quarter the frequency of theclock 55, is connected to supply trigger pulses to set the flip-flop 53and also to count another four-bit binary counter 57. The counter 57 hasa reset terminal which is connected to the 6 output of the flip-flop 52.Thus, the counter 57 will start counting timing pulses from the counter56 as soon as the flip-flop 52 is set by a pulse on the common output 50from the jumper panel 42. The four outputs of the counter 57 areconnected to a NAND gate 58. The NAND gate 58, which normally has a highoutput, will have a low output when the counter 57 is counted up bysixteen trigger pulses from the counter 56. After sixteen counts, thefour outputs of the binary counter 57 will all be high. On the count of16, the momentary low output from the NAND gate 58 passes a pulsethrough a capacitor 59 and an inverter 60 for generating a pulseto clearthe flip-flops 52 and 53. Thus, the flip-flop 53, once set by theflip-flop 52, will remain set for a count of 16 pulses from the binarycounter 56 and then the flip-flop 53 will be cleared.

The clock 55 and the binary counter 56 are also used for generatingother timing signals for operating the voltage-to frequency converter 25and the motor drive logic 26. The eight output of the four-bit binarycounter 56 applies timing pulses to a clock line 61. The four output ofthe counter 56 is connected to the trigger input of a flip-flop 62. The6 output of the flip-flop 62 supplies clock pulses to a clock line 63.Similar pulse trains will appear on the clock lines 61 and 63. However,the time required to set and to clear the flipflop 62 causes a slightphase lag in the pulse train on the clock line 63. Connections to theclock lines 61 and 63 will be discussed below under the description forFIG.

A circuit for generating a continuous analog. signal proportional to theweight of material on a segment of the belt conveyor is shown in detailin FIG. 3. The instantaneous weight of the material on the conveyor beltsegment is sensed by the load cell 17 which comprises a bridgearrangement of four strain gauges 69. Although only a single load cell17 is shown, several load cells may be connected in parallel. Power issupplied to the load cell 17 from the gated power supply 18. The powersupply 18, as well as all other power supplies for operating the scale10, are preferably designed to track or follow a single referencevoltage to minimize measurement errors caused by voltage fluctuations invarious parts of the scale 10. When the gated power supply 18 is on, theload cell 17 has low voltage positive and negative outputs and 71. Thevoltage appearing across the outputs 70 and 71 of the load cell 17 willbe proportional to the total load on the load cell 17.

The outputs 70 and 71 from the load cell 17 are connected, respectively,to inputs of a pair of operational amplifiers 72 and 73. The gain of theamplifier 72 is determined by the ratio of the feedback resistor 74 andresistor 76. The resistor 74 is connected between the output and aninput of the amplifier 72. Similarly, the

gain of the amplifier 73 is determined by the ratio of the feedbackresistor 75 and resistor 76. The resistor 75 is connected between theoutput and an input of the amplifier 73. These inputs of the amplifiers72 and 73 are also interconnected by means of a resistor 76. The outputof the amplifier 73 is connected through a resistor 77 to one input ofan operational amplifier 78 and the output of the amplifier 72 isconnected through a voltage divider including a resistor 79 and apotentiometer 80 to a second input of the amplifier 78. Thepotentiometer 80 is used to balance the two inputs to the amplifier 78such that the output of the amplifier 78 is a function of the differencebetween the outputs of the two amplifiers 72 and 73. A feedback resistor81 is placed between the output and one input of the amplifier 78 forcontrolling the gain of the amplifier 78. The amplifiers 72, 73 and 78function together as the preamplifier l9-for the low level output signalfrom the load cell l7.the preamplifier 19 may have a total gain on theorder of 300 or more.

The output of the amplifier 78 is connected sequentially through aresistor 82, an operational amplifier 83, a resistor 84, a normallyclosed switch 85 and an amplifier 86 to a terminal 87. The amplifier 83establishes the span or range of the analog signal which is proportionalto the weight of material on the load cell 17. A potentiometer 88 isconnected across a low voltage source for applying a controlled voltagethrough a resistor 89 and the switch 85 to the input of the amplifier86. The potentiometer 88 provides an adjustment for initially settingthe analog output at the terminal 87 to zero when no load is applied tothe load cell 17. The negative output of the gated power supply 18 isconnected through a variable resistor 90 to an input of the amplifier83. The variable resistor 90 forms an initial or course adjustment forthe span of the analog weight signal applied to the terminal 87. Avariable feedback resistor 91 is connected between the output and oneinput of the amplifier 83 for controlling the gain of the amplifier 83,thus functioning as a fine span adjustment. After the analog signal onthe terminal 87 is initially set to zero with no material on the beltconveyor, a known weight near the maximum capacity of the belt conveyoris placed on the load cell 17 and the variable resistors 90 and 91 areused to calibrate the analog signal on the terminal 87 to apredetermined level for the known weight on the load cell 17.

The effects of transient conditions such as heat, voltage variations andthe ageing of circuit components in the amplifiers 72, 73, 78 and 83 maycause the analog weight signal applied to the terminal 87 to drift fromits initial zero setting. An automatic zeroing circuit is thereforeprovided to compensate for these transient conditions. The output of theamplifier 83 is connected through an normally open switch 92 and aresistor 93 to the input of an operational amplifier 94. A capacitor 95is placed between the input and the output of the amplifier 94 to causethe amplifier 94 to store the signal applied to its input. The output ofthe amplifier 94 is connected through a resistor 96, an invertingamplifier 97 and a resistor 98 back to the input of the amplifier 83. Afeedback resistor 99 is placed in parallel with the amplifier 97 forcontrolling the gain of the amplifier 97. When the gated power supply 18is turned off to remove power from the load cell 17 and the amplifier 83and subsequently the switch 92 is closed, the amplifier 94 stores theunwanted output of the amplifier 83 until the capacitor is charged to asteady state level determined by the unwanted output of the amplifier83. If the switch 92 is then opened, the amplifier 94 will have asubstantially constant output determined by the charge on the capacitor95. The discharge rate of the capacitor 95 is quite slow due to the veryhigh input impedance of the operational amplifier 94. The output of theamplifier 94 is inverted by an amplifier 97 and applied to the input ofthe amplifier 83 to bring the output of the amplifier 83 to apredetermined constant level. when the gated power supply 18 is againturned on, the amplifier 83 will have an input comprising the sum of theananlog load cell voltage applied through the resistor 82, the spancontrol voltages from the variable resistors 90 and 91 and the automaticzero voltage applied from the amplifier 97 through the resistor 98.

The switches 85 and 92 are preferably electronic switches ofconventional design, such as field effect transistors. The switches 85and 92 and the gated power supply 18 are controlled by a timing circuit100 as shown in FIG. 6. The timing circuit 100 controls cycling of theautomatic zero circuit at a convenient rate, for example times persecond. A 60 Hz. commercial power source 101 may, for example, beconnected through a one-shot multivibrator 102 for generating 120 pulsesper second to periodically trigger the timing circuit 100. The timingpulses generated by the oneshot multivibrator 102 are shown at A on thegraph in FIG. 6. Upon the occurrence of a timing pulse from themultivibrator 102, the timing circuit 100 opens the switch 85 todisconnect the amplified analog load cell signal from the amplifier 86.The timing of the operation of the switch 85 is shown at B in FIG. 6.Subsequent to the opening of the switch 85, the power supply 18 is gatedOK, as shown at C in FIG. 6, by the timing circuit 100 to remove powerfrom the load cell 17 and from the course span control resistor 90. Whenthe power supply 18 is gated off, the amplifier 83 may have anundesirable output because of voltage transients, temperature drift orcomponent ageing. At this time, the timing circuit 100 closes the switch92 to connect the automatic zeroing circuit to the output of theamplifier 83. Timing of the operation of the switch 92 with respect tothe power supply 18 and the switch 85, is shown at D in FIG. 6. When theswitch 92 is closed, the amplifier 94 will rapidly store the output ofthe amplifier 83 until the charge on the capacitor 95 reaches a steadystate condition, at which time the amplifier 94 will have a steadyoutput. This output is inverted by the amplifier 97 and applied throughthe resistor 98 to the input of the amplifier 83 to cancel or zero theunwanted component of the output of the amplifier 83. The switch 92 isthen opened by the timing circuit 100. Immediately after the switch 92is opened, the power supply 18 is gated on and, subsequently, the switch85 is closed to again apply an analog output signal from the amplifier83 to the input of the amplifier 86.

While the output from the amplifiers 72, 73, 78 and 83 is beingautomatically zeroed, it is apparent that the signal applied to theterminal 87 will be at zero due to the opening of the switch 85. Thus,the signal applied to the terminal 87 would be expected to have gaps, asshown in B of FIG. 6, resulting from operation of the switch 85.However, the amplifier 86 is provided with a capacitor 103 and aresistor 104 to fill the gaps caused by the opening the switch 85. Theresistor 104 is connected from the output of the amplifier 86 throughthe switch 85 to the input of the amplifier 86 to control the gain ofthe amplifier 86 when the switch 85 is closed. The capacitor 103 isconnected directly between the input and the output of the amplifier 86.During the time that the switch 85 is closed, the capacitor 103 will becharged to a substantially steady state condition determined by theinput and output of the amplifier 86. When the switch 85 is opened bythe timing circuit 100, the steady state charge on the capacitor 103will cause the amplifier 86 to maintain or hold its output, therebyfilling gaps which would otherwise occur in the analog weight signal onthe terminal 87.

During this time, the charge on the capacitor 103 will be maintainedsubstantially constant due to the extremely high input impedance of theoperational amplifier 86. Thus, the terminal 87 will see a substantiallycontinuous analog signal which will vary as the load on the load cell 17varies.

As stated above under the description of the block diagram of FIG. 1,the analog weight signal is used to modulate the constant width,frequency modulated pulse train. It will be appreciated that the timingcircuit 100 may be triggered directly by the pulse train from theterminal 54. If the automatic zero circuit is triggered immediatelyafter each pulse on the terminal 54 and the automatic z'er'o cycle iscompleted in a time interval shorter than the shortest interval betweenthe pulses, the switch 85 and the gap fill circuit may be eliminated.The elimination of the switch 85 and the gap fill circuitry will causethe analog output on the terminal 87 to be interrupted each time theanalog weight signal is automatically zeroed. However,the interruptionswill occur only while there is no output pulse on the terminal 54. Sincethe analog signal on the terminal 87 is used to modulate the amplitudeof the constant width pulses, it is apparent that the interruptions ofthe analog weight signal on the terminal 87 will not affect operation ofthe integrating scale 10.

Turning to the circuit of FIG. 4 and the related graph of FIG. 4a, theanalog weight signal on the terminal 87 is applied through a resistor 110 to the source electrode of a field effect transistor 1 l l. Theoutput appearing at the drain electrode of the field effect transistor111 will depend upon the voltage applied to the gate electrode. The edgeelectrode is normally connected through a resistor l 12 to a l 5 voltpower supply so that the transistor 111 is normally biased into .anonconducting state. However, the gate electrode is also connectedthrough a transistor 113 to ground. The base of the transistor 113 isconnected through a bias resistor 114 to the volt power source andthrough a resistor l 15 to the terminal 54 connected to the 0 output ofthe flip-flop 53 in FIG. 2. A typical speed pulse train appearing on theterminal 54 is shown at A in FIG. 4a. This pulse train occurs whenmaterial is transferred at a predetermined fast speed prior to the timet, and at half that rate after the time t,. During the constant widthpulses generated by the flip-flop 53, the base of the transistor 1 13 isgrounded through the resistor 115,

biasing the transistor 113 into a conducting state. When the transistor113 conducts to connect the gate of the field effect transistor 111 toground, a voltage will appear on the drain electrode of the transistor111 which is proportional to the analog weight signal on the terminal87. A typical analog weight signal on the terminal 87 is shown at B inFIG. 4a. This signal is shown as being constant prior to the time i, toindicate a constant weight and as gradually increasing after the time tto indicate that the weight is increasing. The output or drain electrodeof the transistor 1 1] is connected to an input of an operationalamplifier 116. The signal applied to the amplifier 116 is shown at C inFIG. 4a. It will be noted that the pulse spacing in C increases with adecrease in the material transfer speed and that the pulse magnitudeincreases with an increase in weight.

From the above description, it is apparent that the input to theamplifier 116 is, in effect, the constant width pulse train on theterminal 54 modulated or multiplied by the analog weight signal on thetenninal 87. However, the field effect transistor 111 does not haveinfinite resistance when biased into a nonconducting state. A portion ofthe analog weight signal on the terminal 87 would tend to pass throughthe transistor 111 even though it is in its nonconducting condition.Therefore, a transistor 117 is provided to ground the source electrodeof the transistor 11] during the time interval between the constantwidth pulses on the terminal 54. The terminal 54 is connected through adiode 118 and a resistor 119 to the base of the transistor 117. A biasresistor 120 is also provided to connect the base of the transistor 117to ground. During the variable time inter'vals between the constantwidth pulses on the terminal 54, the transistor 117 conducts to groundthe source electrode of the field effect transistor 111. While thetransistor 117 is conducting, the analog weight voltage on the terminal87 will appear across the resistor and no signal will pass through thetransistor 111 to the input of the amplifier 116.

The gain of the amplifier 116 is determined by the feedback resistancebetween the output and the input of the amplifier 116 and the resistancein the input circuit of the amplifier 116. The input resistance of theamplifier 116 consists of the sum of the resistor 110 and the resistancebetween the source and drain electrodes of the field efiect transistor111 when the gate electrode is grounded through the transistor 113. Un-

fortunately, the resistance of the field effect transistor 111 isaffected by temperature. Therefore, a resistor 121 and a similar fieldeffect transistor 122 are connected in series between the output and theinput of the amplifier 116. The gate electrode of the field effecttransistor 122 is grounded so that the two field effect transistors 111and 122 will have a similar change in forward resistance when heatedthrough the same temperature change. Through the use of the field effecttransistor 122 in the feedback circuit for the amplifier 116, theamplifier 116 will have a temperature compensated output equal to theproduct of the constant width pulse train which has a frequency orrepetition rate proportional to the speed of the belt conveyor and theanalog signal which has a voltage proportional to the weight of materialon a segment of the belt conveyor.

The average value of the modulated pulse train appearing at the output'of the amplifier 116 is proportional to the rate at which material istransferred on the belt conveyor. The modulated pulse train at theoutput of the amplifier 116 is averaged or filtered by means of a highlydampened amplifier 123. The output of the amplifier 1 16 is connectedthrough a pair of series connected resistors 124 and 125 to one input ofthe amplifier 123. The second input of the amplifier 123 is connectedthrough a resistor 126 to ground. A capacitor 127 is connected frombetween the two series resistors 124 and 125 to ground. A portion of theoutput of the amplifier 123, as determined by a voltage dividerconsisting of a variable resistor 128 and a fixed resistor 129 connectedin series between the output of the amplifier 123 and ground, is fedback to the input of the amplifier 123. The junction between thevariable resistor 128 and the fixed resistor 129 is connected through acapacitor 130 to the input of the amplifier 123 and is also connectedthrough a resistor 131 to the junction between the series resistors 124and 125. When a high input signal is applied to the amplifier 123, thecapacitor 130 is charged at a rate determined by the time constant ofthe capacitor 130 and the variable resistor 128. Between pulses at theoutput of the amplifier 1 16, the capacitor 130 is slowly dischargedthrough the series resistors 131 and 125. The capacitor 127 also dampenschanges in the input to the amplifier 123. In view of the dampeningeffect of the capacitor 130 and the capacitor 127, the amplifier 123will apply to a terminal 132 acontinuous analog signal which isproportional to the rate at which material is transferred on the beltconveyor.

The analog rate signal on the terminal 132 may be integrated over aperiod of time for measuring the total weight of material transferredover such period of time, or the rate signal may be amplified anddisplayed on a rate meter. The rate signal on the terminal 132, ofcourse, may also be used as a control signal for apparatus external tothe scale 10, namely, for controlling the speed of the belt conveyor,for operating a recorder or for any other necessary control function.The span of the rate signal on the terminal 132 is adjusted by means ofthe variable resistor 128. The resistor 128 may, for example, be setsuch that ten volts will appear on the terminal 132 when the beltconveyor is operating at its maximum capacity.

As stated above, one use of the rate signal on the terminal 132 is tooperate a new meter. The terminal 132 may be connected through aresistor 133 to one input of an amplifier 134. A feedback resistor 135is connected between the output of the amplifier 134 and a second inputto the amplifier 134. The second input is also connected through aresistor 136 to ground. The output of the amplifier 134 is connectedthrough a resistor 137 to the input of an amplifier 138. A capacitor 139is connected between the output and the input of the amplifier 138. Avariable resistor 140 is connected between the output of the amplifier138 and the input of the amplifier 134 which is connected to theresistor 133. The variable resistor 140 controls the total gain of thetwo amplifiers 134 and 138 for providing a fine control over the span ofthe rate displayed on the rate meter 24. The output of the amplifier138, which is an analog rate signal, is applied through a variableresistor 141 to the meter 24. The variable resistor 141 is provided tocontrol the span of the meter 24. The output of the amplifier 138 isalso connected to a terminal 142 which will be discussed further belowunder the discussion of FIG. 5. The various controls and calibrationadjustments in the scale 10 permit calibrating the meter 24 to read inany desired units, such as pounds per second, pounds per minute, tonsper minute, tons per hour, etc. The scale 10 may also be easilycalibrated so that the full scale reading of the meter 24 corresponds tothe maximum transfer rate for any conveyor to which the scale 10 isattached.

Referring now to FIG. 5, the analog rate signal on the terminal 132(from FIG. 4), is applied through a resistor 148 to a summing junction149. The summing junction 149 is also connected through a resistor 150to the tap or variable terminal 151 on a potentiometer 152. The ends ofthe potentiometer 152 are connected to the plus and minus terminals of a15 volt regulated voltage source (not shown). The tap terminal 151 isset to the center of the potentiometer 152.

The voltage appearing on the summing junction 149 is integrated by meansof an amplifier 153 and a parallel feedback capacitor 154. The output ofthe integrator 153 is connected through a resistor 155 and anoperational amplifier 156 to a junction 157. A feedback resistor 158 isconnected between the output and the input of the amplifier 156 tocontrol the gain of the amplifier 156. The junction 157 at the output ofthe amplifier 156 is connected through a resistor 159 to the negativeinput of an operational amplifier 160 and from the input of suchamplifier 160 through a resistor 161 to the positive terminal of the 15volt reference source. Similarly, the junction 157 is connected througha resistor 162 to the positive input of an operational amplifier 163 andfrom the input of such amplifier 163 through a resistor 164 to thenegative terminal of the 15 volt reference source. It is apparent thatthe four series resistors 161, 159, 162 and 164 extending between thepositive and negative terminals of the 15 volt reference source form avoltage divider. The resistor 161 and 164 are of the same value and theresistors 159 and 162 are of the same value. As a consequence of this,the negative input of the amplifier 160 will normally be at a positivevoltage with respect to the junction 157 and the positive input of theamplifier 163 will normally be at a similar, but negative voltage withrespect to the junction 157. Both of the amplifiers 160 and 163 will,therefore, normally be switched off. Feedback for the amplifier 160is-provided through a Zener diode 165 connected between the output ofthe amplifier 160 and the negative input of the amplifier 160. Thepositive input of the amplifier 160 is grounded through a resistor 167.The input of the amplifier 160 is clamped by diodes 166 and to aspecified voltage level. Feedback for the amplifier 163 is providedthrough a Zener diode 168 connected between the output and thenegativeinput of the amplifier 163. The negative input of the amplifier 163 isalso connected through a resistor 169 to ground.

As previously stated, the negative input of the amplifier 160 isnormally maintained positive by the 15 volt reference source, and isclamped to a specified voltage level by the diodes 166 and 170. Thepositive input of the amplifier 163, which is normally maintainednegative by the 15 volt reference source, is clamped to a specifiedvoltage level by two diodes 171 and 172. When the integrating amplifier153 integrated a positive voltage on the summing junction 149, anincreasingly positive voltage is applied to the junction 157. Thisvoltage will cause current to initially flow through the resistor 162and subsequently through the resistor 162 and the diode 172 when thecurrent through the resistor 162 is greater than the currentthrough theresistor 164, with the voltage on the positive terminal of the amplifier163 going from negative towards positive. Current will also flow throughthe resistor 159 and the diode 166. As the positive input of theamplifier 163 is driven positive, the output of the amplifier 163 willbe driven positive. The amplifier 163 will initially have an extremelyhigh gain due to the fact that Zener diode 168 is not conducting. Theoutput of the amplifier 163 will rapidly increase until the breakdownvoltage of the Zener diode 168 is reached. As soon as this condition isreached, the output of the amplifier 163 will be stabilized because ofthe voltage regulating properties of Zener diodes. The output of theamplifier 163 is connected through a resistor 173 to the J input of aflipflop 174. A high input will be maintained on the flipflop 174 aslong as the positive input of the amplifier 163 is maintained at apositive voltage.

If, on the other hand, a negative signal is applied from the terminal132 to the summing junction 149, the integrating arnplifier 153 and theamplifier 156 will apply a negative signal on the junction 157. Thenegative signal on the junction 157 will cause current to initially flowthrough the resistor 159 and subsequently through the resistor 159 andthe diode 170 when the current through the resistor 159 is greater thanthe current through the resistor 161 and also through the resistor 162and the diode 171. When the signal on the junction 157 becomessufficiently high, the negative input of the amplifier 160 will bedriven negative. The amplifier 160 will have an extremely high gainuntil its output reaches the breakdown voltage of the Zener diode 165.At this point, feedback current will flow through the Zener diode 165 tostabilize the output of the amplifier 160. The output of the amplifier160 is connected through a resistor 175 to the J input of a flip-flop176. The signal will be maintained on the input of the flipflop 176 onlyas long as the negative input of the amplifier 160 is maintained at anegative voltage. [t is readily apparent that, at most, only one of theflip-flops 174 and 176 may have a signal on its J input. The K input ofeach of the flip-flops 174 and 176 are connected together to a positivevoltage source such that these flipflops are normally cleared when asignal is not applied to the J input.

The Q output of the flip-flop 174 controlsa switch 177 to connect the lvolt terminal of the reference source through a resistor 178 to thesumming jucntion 149. Similarly, the Q terminal of the flip-flop 176controls a switch 179 to connect the positive terminal of the 15 voltreference source through a resistor 180 to the summing junction 149.'Theswitches 177 and 179 may be of any conentional design and may, forexample, each consist of a field effect transistor. After the amplifier153 integrates a positive signal on the junction 149 until the amplifier163 is turned on and the flip-flop 174 is set, the switch 177 is closedto connect the negative terminal of the IS volt reference to the summingjunction 149. At this instance, the polarity of the voltage on thejunction 149 changes, causing a reversal in the slope of the changingoutput of the intergrating amplifier 153. If, on the other hand, theintegrator 153 integrates a negative signal on the junction 149 untilthe amplifier 160 turns on and the flip-flop 176 is set, the switch 179connects the positive terminal of the 15 volt reference source to thesumming junction 149 and, again, the slope of the changing output of theintegrator 153 reverses.

The flip flops 174 and 176 are triggered by means of a square wave clockpulse signal on the clock line 61 (from FIG. 2). A portion of the squarewave clock signal on the line 61 is shown graphically at A in FIG. 7. Inthe following discussion, we will assume that the analog rate signalapplied on the tenninal 132 is positive and of a relatively low voltageindicating a relatively low forward transfer rate. The integrator 153will integrate this signal over a period of time to cause the amplifier156 to apply an increasingly positive voltage on the junction 157. Suchan increasing voltage is shown in the segment 184 in the graph B on FIG.7. Integration will continue in this direction for the time interval t,.The interval t ends when the voltage shown by the dahsed line exceeded,causing the amplifier 163 to suddenly turn on and apply a signal to' theJ input of the flip-flop 174 and a trigger pulse is applied on the clockline 61 to the flip-flop 174. when these two conditions occur, theflip-flop 174 is set, closing the switch 177. Closure of the switch 177connects the negative terminal of the reference source to the summingjunction 149, causing the integrator 153 to integrate the differencebetween the l5 volt reference and the low voltage positive analog ratesignal on the line 132. As shown in the graph B in FIG. 7, the slope ofthe changing voltage on the junction 15 7 is reversed. This voltage isshown in the segment 186.

After the switch 177 is closed and the direction of the integrationreverses, the voltage on the junction 157 rapidly drops below thevoltage 185 required to maintain the amplifier 163 in an on state. As aconsequence of the ampiifier 163 turning off, the next clock pulse onthe line 61 resets or clears the flip-flop 174, opening the switch 177.Thus the flip-flop 174, or the flip-flop 176, will be set, at most, forthe time required for one clock pulse on the line 61. The flip-flop 174will remain in a cleared state for a time interval proportional to theanalog rate signal on the terminal 132. This is shown in graph B in FIG.7 where the flip-flop 174 is maintained off for the indefinite timeinterval t and is on for the fixed time interval t, which is equal tothe time of one clock pulse.

If the analog rate signal applied on the terminal 132 increases in valuetowards its maximum voltage, the voltage applied to the junction 157 atthe output of the amplifier 156 appears as is shown by the segment 187in graph C of FIG. 7 Here the slope of the integration of the unknown187 has rapidly increased, greatly shortening the time interval t,during which the unknown is integrated. in addition, the slope ofintegration of the difference between thereference and the unknown hasdecreased as shown by the segment 188. The decrease in the slope ofsegment 188 results in-a much smaller voltage change in the output ofthe integrating amplifier 153 during the fixed time interval 1,. Thisdecrease in voltage change further decreasesthe time interval 1,. Thusthe total time interval for one cycle in graph C, or the sum of the twotime intervals t, and t,, is much shorter than the time interval ingraph B.

It will be apparent that the frequency at which the flip-flop 174, orthe flip-flop 176, is turned on and off is proportional to the voltageof the analog rate signal on the terminal 132. If the voltage on theterminal 132 is positive because the material is on the conveyor belt,

only the flip-flop 174 will be periodically set and cleared. If, on theother hand, the voltage on the terminal 132 is negative as a consequenceof no material on the conveyor belt and tension on the load cell 17, theflip-flop 176 will be periodically set and cleared. Thus the twoflip-flops 174 and 176 in combination with the integrator 153 detectwhen the load cells 17 are in compression or tension.

The Q output of the flip-flop 174 is connected to the J input of aflip-flop 191 and the Q output of the flipflop 176 is connected to the Kinput of the flip-flop 191. The clock pulse line 63 is connected to thetrigger input of the flip-flop 191. On the next clock pulse after theflip-flop 174 is set, the flip-flop 191 will be set and will remain setuntil the occurrence of a clock pulse while the flip-flop 176 is set.The state in which the flipflop 191 is set determines the direction inwhich the counter 28 is counted.

The counter 28 is driven by the motor 27, which is a four-phase steppingmotor. The motor 27 has four windings 192-195, two of which are alwaysenergized. Stepping of the motor 27 is accomplished by deenergizing oneof the coils and energizing another of the coils. Thus, if the coils 192and 194 are initially energized, the motor 27 is stepped forward bydeenergizing the coil 194 and energizing the coil 195 while the coil 192is maintained in an energized state. Or, the motor 27 may be stepped ina reverse direction by de-energizing the coil 192 and energizing thecoil 193, while maintaining the coil 194 energized. One end of each ofthe coils 192-195 is connected in common to a suitable power source andthe other ends of the coils 192-195 are connected through an electronicswitch 196-199, respectively, to ground. The switches 196-199 may, forexample, consist of transistors. The switches are energized by the fouroutputs of two flipflops 200 and 201. The Q output of the flip-flop 200controls the switch 197 and the 6 output of the flipflop 200 controlsthe switch 196. Similarly, the Q output of the flip-flop 201 controlsthe switch 199 and the 6 output of the flip-flop 201 controls the switch198. Since one of the outputs of each of the two flip-flops 200 and 201is always set, one of the switches 196 and 197 will always be energizedby the flip-flop 200 and one of the switches 198 and 199 will always beenergized by the flip-flop 201. Thus, one of the motor windings 192 and193 is always energized and one of the motor windings 194 and 195 isalways energized.

The states of the flip-flops 200 and 201 are controlled by a logicnetwork including four AND gates 202-205. The outputs'of the AND gates202 and 203 are connected through a NOR gate 206 to the K input of theflip-flop 200 and also through the NOR gate 206 and through an inverter207 to the J input of the flipflop 200. Similarly, the outputs of theAND gates 204' and 205 are connected through a NOR gate 208 to the Kinput of the flip-flop 201 and the output of the NOR gate 208 is alsoconnected through an inverter 209 to the J input of the flip-flop 201.The AND gate 202 has two inputs, one connected to the Q output of thedirection control flip-flop 191 and one connected to the Q output of theflip-flop 201. The two inputs of the AND gate 203 are connected to the 6output of the direction control flip-flop 191 and the 6 output of theflip-flop 201. The two inputs of the AND gate 204 are connected to the 6output of the direction control flip-flop 191 and to the Q output of theflip-flop 200. Finally,

the two inputs of the AND gate 205 are connected to the Q output of thedirection control flip-flop 191 and to the 6 output of the flip-flop200. The flip-flops 200 and 201 are triggered by pulses on a triggerline 210.

in operation of this logic network, assume that the counter is tooperate in a forward direction and, therefore, that the directioncontrol flip-flop 191 is set to a high 0 output. The Q output of thedirection control flip-flop 191 enables the AND gates 202 and 205. If weinitially assume that both of the flip-flops 200 and 201 are cleared,then the AND gate 205 will have two high inputs and a high output. Thehigh output of the AND gate 205 will cause the NOR gate 208 to have alow output and thus the inverter 209 will apply a signal to the J inputof the flip-flop 201. Both of the AND gates 202 and 203 will have lowoutputs, causing the NOR gate 206 to apply a high signal to the K inputof the flipflop 200. On'the occurrence of the next pulse on the triggerline 210, the flip-flop 201 will be set, causing the switch 198 to openand the switch 199 to close. The switch 196 remains closed since theflip-flop 200 remains cleared. Setting of the flip-flop 201 applies ahigh signal to the second input of the gate 202, causing the NOR gate206 to have a low output and the inverter 207 to apply a signal to the Jinput of the flip-flop 200. There has been no change in the signal onthe inputs on the gate 205, so the inverter 209 maintains the signal onthe J input of the flip-flop 201. Therefore, the next pulse on thetrigger line 210 sets the flip-flop 200, thereby closing the switch 197and opening the switch 196. Setting the flip-flop 200 also removes oneinput from the AND gate 205, causing the next trigger pulse on the line210 to clear the flip-flop 201. Thus, it will be apparent that thetrigger pulses alternately set and clear the two flip-flops 200 and 201.If the direction control flip-flop 191 had been cleared to a high 6state due to the detection of a negative load, the AND gates 202 and 205would be inhibited and the AND gates 203 and 204 would each have a highinput. This would cause the flip-flops 200 and 201 to still bealternately set and cleared, but in a reverse direction to reverse thedirection in which the motor 27 operates the counter 28.

As previously stated, one of the flip-flops 174 and 176 is alternatelyset and cleared at a frequency proportional to the rate at whichmaterial is conveyed. The flip-flops 174 and 176 are used as a signalsource to control pulses on the trigger line 210 for the flip-flops 200and 201 and, thus, to control the rate at which the motor 27 steps thecounter 28(Since one of the flipflops 174 and 176 is always clearedwhile the other of the flip-flops 174 and 176 is alternately cleared andset, the O outputs of each of the flipflops 174 and 176 are connected toa NAND gate 211. The NAND gate 211 will have a low output when both ofthe flip-flops 174 and 176 are cleared during integrationof the analograte signal on the terminal 132. During integration of the reference,one of the flip-flops 174 or 176 will be set and the NAND gate 211 willhave a high output. The output of the NAND gate 211 is connected througha NAND gate 212 and a jumper wire 213 through a pair of inverters 214and 215 to the trigger line 210. The second input of the NAND gate 212isnormally high. Therefore, the NAND gate 212 will have an output which isswitched when the output of the NAND gate 211 is switched by theflip-flops 174 and 176. Therefore, a signal is applied on the triggerline 210 which is switched whenever the NAND gate 211 is switched by theflip-flops 174 and 176.

It will be apparent that the range of the counter 28 may be increased bya predetermined factor by dividing the pulses on the line 210 by such afactor. If, for example, the output of the NAND gate 211 is switchedtwice for each time the signal on the trigger line 210 is switched (thepulse count is divided in half), the range of the counter 28 will bedoubled. It has therefore been found desirable to include an integratingfactor circuit 216 for dividing the pulse output of the NAND gate 211 bypredetermined factors of, for example, one, two, four, eight, 16 and 32to increase the range of the counter 28 by such factors. The output ofthe NAND gate 212 is connected to the trigger input of a four-bit binarycounter 217. The jumper 213 may be moved to selectively connect one ofthe four outputs of the counter 217 through the inverters 214 and 215 tothe trigger line 210 to selectively divide the output of the gate 212 byfactors of two, four, eight and 16. The divide-by-l6 output of thecounter 217 is also connected to trigger a flip-flop 218 to provide adivide-by-32 factor. If the jumper 213 is moved from the output of theNAND gate 212 to connect the first output of the counter 217 to theinverter 214, the output of the NAND gate 211 must be switched twice foreach time the signal on the trigger line 210 is switched.

When the conveyor is empty, or nearly empty, transient conditions maycause the counter 28 to erroneously indicate that a small amount ofmaterial has been conveyed. Therefore, circuitry has been provided toblock or inhibit operation of the counter 28 when the conveyor isoperated below a minimum rate, such as below one 'or two percent of themaximum transfer rate. The analog rate signal on the terminal 142 (fromFIG. 4) is connected through a resistor 219 to the input of an operationamplifier 220. The input of the amplifier 220 is also connected througha pair of reverse biased parallel diodes 221 and 222 to ground to limitthe level of the input. Feedback is provided by means of a Zener diode223. As a consequence, when the amplifier 220 is initially turned on, itwill have an extremely high gain until the breakdown voltage of theZener diode 223 isreached, at which time the output of the amplifier 220is stabilized. The input of the amplifier 220 is also connected througha resistor 224 to a voltage divider comprising a pair of seriesresistors 225 and 226. Selection of the values of the resistors 225 and226 control the voltage required on the terminal 142 to turn theamplifier 220 on. The resistors 225 and 226 are typically selected suchthat the amplifier 220 will be on as long as the analog rate signal onthe terminal 142 exceeds one or two percent of its maximum value. Theoutput of the amplifier 220 is connected to a NOR gate 227. The otherinput of the NOR gate 227 is connected to ground through a switch 228.The normally low output of the NOR gate 227 is connected through aninverter 229 to the NAND gate 212. Thus, whenever the analog rate signalon the terminal 142 is below a predetermined percentage of its maximumvalue, a low signal is applied to the second input of the NAND gate 212to inhibit passage of a pulse signal from the NAND gate lowed to runwhen less than the minimum allowable percentage of the rated capacity ison the beltconveyor. The switch 228 normally connects one input of theNOR gate 227 to ground to inhibit the amplifier 220 during zeroing ofthe scale 10. This is necessary due to the fact that belt conveyorsinherently have a nonuniform weight over their length. If the scale 10is not calibrated for a dynamic zero, the counter 28 will include anerror factor dependent upon the degree of nonuniformity of the conveyor.

It will be appreciated that various changes and modifications may bemade in the scale 10 without departing from the spirit and the scope ofthe claimed invention. In one embodiment, the scale 10 may, for example,be modified to include only the circuitry required for counting ormeasuring the total quantity of material delivered over a period of timewithout indicating the rate at which the material is delivered. Or, inanother embodiment, the scale 10 may be modified to include only thecircuitry required for indicating the transfer rate with the circuitryfor indicating the total quantity of material transferred omitted. Itwill also be readily apparent that although the scale 10 has beendescribed for use with a belt conveyor, it is suitable for use withother types of material conveyors and for measuring quantities otherthan transfer rate and the total quantity of material transferred. If,for example, the tachometer 11 is driven from the output shaft of amotor and the load cell 17 senses the torque output of the motor, thenthe rate meter 24 will indicate the instantaneous power output of themotor. The meter 24 may be calibrated to read in any convenient units,such as horsepower. The counter 28 is then calibrated to indicate thetotal energy output of the motor over a period of time and may indicatethe total foot-pound output of the motor.

It will also be appreciated that measuring apparatus according to thepresent invention may provide various outputs for controlling accessoryequipment. The analog rate signal on the terminal 132 (FIG. 4) may, forexample, dr1ve a recorder or supply a control signal for use incontrolling the conveyor. Or, the counter 28 may be replaced by adigital counter which, for example, supplies a total weight signal to abatching control computer.

What I claim is:

1. Measuring apparatus for use with a conveyor for moving materialthrough a region comprising, in combination, means for generating atrain of constant width pulses which are repeated at a frequencyproportional to the speed at which the material is transferred throughthe region, means for generating an analog signal proportional to theinstantaneous weight of material in the region, multiplying meansresponsive to the analog weight signal and to the pulse train forgenerating a modulated pulse train corresponding to the product of theanalog weight signal and the pulse train, and means for measuring theaverage value of the modulated pulse train, whereby such average valueis proportional to the rate at which material is transferred through theregion. I

2. Measuring apparatus for use with a conveyor for moving materialthrough a region, as defined in claim 1 wherein said multiplying meansincludes switch means responsive to the pulse train for selectivelypassing and blocking the analog weight signal, said switch means passingthe analog weight signal during the constant width pulses in the pulsetrain and blocking the analog weight signal between the constant widthpulses.

3. Measuring apparatus, as defined in claim 1, wherein said measuringmeans includes means for filtering the modulated pulse train to obtain acontinuous analog signal proportional to the material transfer rate, andmeans responsive to the continuous analog signal for indicating suchmaterial transfer rate.

4. Measuring apparatus for use with a conveyor for moving materialthrough a region, as defined in claim 3, further includingvoltage-to-frequency converter means responsive to said continuousanalog signal for generating a frequency modulated pulse train having afrequency proportional to said transfer rate.

5. Measuring apparatus for use with a conveyor for moving materialthrough a region, as defined in claim 4, further including steppingmotor means responsive to said frequency modulated pulse train andcounting means driven by said stepping motor means for indicating thetotal weight of material conveyed by the conveyor over a period of time.

6. Measuring apparatus, as defined in claim 3, and including means forchanging the pulse rate of the train of constant width pulses by apredetermined factor whereby the average value of the continuous analogsignal is changed by such predetermined factor, and means for changingthe predetermined factor.

7. Measuring apparatus, as defined in claim 1, wherein said measuringmeans includes means for filtering the modulated pulse train to obtain acontinuous analog signal proportional to the material transfer rate,means for integrating the continuous analog signal, and

means for measuring the total quantity of material conveyed through theregion over a period of time by measuring the integral of the continuousanalog signal over such period of time.

8. Measuring apparatus, as defined in claim 7, and including means forchanging the pulse rate of the train of constant width pulses by apredetermined factor whereby the measure of the total quantity ofmaterial conveyed is changed by such predetermined factor, and means forchanging the predetermined factor.

9. Measuring apparatus, as defined in claim 7, wherein said integratingmeans includes converter means for generating a pulse signal having apulse rate proportional to the continuous analog signal, and whereinsaid means for measuring the total weight of conveyed material includesmeans for counting pulses in the pulse signal whereby the pulse count isproportional to the total weight of conveyed material.

10. Measuring apparatus, as defined in claim 9, and including means forchanging the number of pulses in the pulse signal by a predeterminedfactor whereby the weight range covered by said counting means ischanged.

11. Measuring apparatus, as defined in claim 9, and including means forinhibiting the operation of said counter means when said conveyor ismoving material at less than a predetermined minimum rate.

12. Measuring apparatus, as defined in claim 7, and including means forinhibiting the operation of said means for measuring the total weight ofconveyed material when the material is conveyed at less than apredetermined minimum rate.

13. Measuring apparatus, as defined in claim 1, and including a powersource, means for operating said analog signal generating means for saidpower source, means for periodically interrupting power from said powersource to said analog signal generating means, and means operable whilepower to said analog signal generating means is interrupted for settingthe output of said analog signal generating means to zero.

14. Measuring apparatus, as defined in claim 13, wherein said powerinterrupting means interrupts power to said generating means onlybetween the constant width pulses in the pulse train.

15. Measuring apparatus, as defined in claim 13, and including meansoperable while power to said analog signal generating means isinterrupted for maintaining said modulated pulse train at its amplitudeprior to the power interruption.

16. A method for measuring the quantity of material transferred througha region, comprising the steps of:

a. generating a train of constant width pulses having a frequencyproportional to the speed at which material is transferred through theregion;

b. modulating the amplitude of the pulse train in proportion to theinstantaneous weight of material in the transfer region: and

c. filtering the modulated pulse train to produce a continuous signalproportional to the product of the weight of material in the regiontimes the transfer speed, whereby the magnitude of the filtered signalis a measure of the instantaneous rate at which material is transferredthrough the region.

17. A method for measuring the quantity of material transferred througha region, as set forth in claim 16, and further including the steps of:

d. converting the filtered signal into a second pulse train having apulse rate proportional to the magnitude of the filtered signal; and

e. totalizing the pulses in such second pulse train as a measure of thetotal quantity of material transferred.

5 7w UNl'ifED STATES PATENT OFFICER; v 15, w v j T 1 T mafia-W161 1Tb OF'CGRRELCTIYON Patent NO. 3,754, 126 Dated August 21, 1973 Inventods)Rog'erB. Williams, Jr 7 is crtifid tha t'error ap p earsr in the.afiove-idfifified ptent I that said LettersvPate-nt are herebycorrected as shownbelow:

, Column 20; line 14; "for" should-read from Signed-and seale d' this"1st day of JanuarylQ'ZLL. 7

(SEAL) Attest:

EDWARD M.FL ETCHE ,'JR., RENE DQTEGTMEXER" 1 Attesting Officer Acting'(Jommis siqner of Patents 5 9 UNrsiEn STATES PATENT oEEmE CERTXFKCATE9F CORRECHON Patent No. 3.754, 126 Dated August 21, 1973 I v n -075(5)Roger B. Williams, Jr.

1; is certified that error appears in the above'identifiec1 patent an;mat said Letters Patent are hereby corrected as shown below:

Column 20, line 14, "for" should read from Signed and sealed this lstday of January 197L (SEAL) Attest:

EDWARD M.FLETGHER,JR. RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents

1. Measuring apparatus for use with a conveyor for moving materialthrough a region comprising, in combination, means for generating atrain of constant width pulses which are repeated at a frequencyproportional to the speed at which the material is transferred throughthe region, means for generating an analog signal proportional to theinstantaneous weight of material in the region, multiplying meansresponsive to the analog weight signal and to the pulse train forgenerating a modulated pulse train corresponding to the product of theanalog weight signal and the pulse train, and means for measuring theaverage value of the modulated pulse train, whereby such average valueis proportional to the rate at which material is transferred through theregion.
 2. Measuring apparatus for use with a conveyor for movingmaterial through a region, as defined in claim 1 wherein saidmultiplying means includes switch means responsive to the pulse trainfor selectively passing and blocking the analog weight signal, saidswitch means passing the analog weight signal during the constant widthpulses in the pulse train and blocking the analog weight signal betweenthe constant width pulses.
 3. Measuring apparatus, as defined in claim1, wherein said measuring means includes means for filtering themodulated pulse train to obtain a continuous analog signal proportionalto the material transfer rate, and means responsive to the continuousanalog signal for indicating such material transfer rate.
 4. Measuringapparatus for use with a conveyor for moving material through a region,as defined in claim 3, further including voltage-to-frequency convertermeans responsive to said continuous analog signal for generating afrequency modulated pulse train having a frequency proportional to saidtransfer rate.
 5. Measuring apparatus for use with a conveyor for movingmaterial through a region, as defined in claim 4, further includingstepping motor means responsive to said frequency modulated pulse trainand counting means driven by said stepping motor means for indicatingthe total weight of material conveyed by the conveyor over a period oftime.
 6. Measuring apparatus, as defined in claim 3, and including meansfor changing the pulse rate of the train of constant width pulses by apredetermined factor whereby the average value of the continuous analogsignal is changed by such predetermined factor, and means for changingthe predetermined factor.
 7. Measuring apparatus, as defined in claim 1,wherein said measuring means includes means for filtering the modulatedpulse train to obtain a continuous analog signal proportional to thematerial transfer rate, means for integrating the continuous analogsignal, and means for measuring the total quantity of material conveyedthrough the region over a period of time by measuring the integral ofthe continuous analog signal over such period of time.
 8. Measuringapparatus, as defined in claim 7, and including means for changing thepulse rate of thE train of constant width pulses by a predeterminedfactor whereby the measure of the total quantity of material conveyed ischanged by such predetermined factor, and means for changing thepredetermined factor.
 9. Measuring apparatus, as defined in claim 7,wherein said integrating means includes converter means for generating apulse signal having a pulse rate proportional to the continuous analogsignal, and wherein said means for measuring the total weight ofconveyed material includes means for counting pulses in the pulse signalwhereby the pulse count is proportional to the total weight of conveyedmaterial.
 10. Measuring apparatus, as defined in claim 9, and includingmeans for changing the number of pulses in the pulse signal by apredetermined factor whereby the weight range covered by said countingmeans is changed.
 11. Measuring apparatus, as defined in claim 9, andincluding means for inhibiting the operation of said counter means whensaid conveyor is moving material at less than a predetermined minimumrate.
 12. Measuring apparatus, as defined in claim 7, and includingmeans for inhibiting the operation of said means for measuring the totalweight of conveyed material when the material is conveyed at less than apredetermined minimum rate.
 13. Measuring apparatus, as defined in claim1, and including a power source, means for operating said analog signalgenerating means for said power source, means for periodicallyinterrupting power from said power source to said analog signalgenerating means, and means operable while power to said analog signalgenerating means is interrupted for setting the output of said analogsignal generating means to zero.
 14. Measuring apparatus, as defined inclaim 13, wherein said power interrupting means interrupts power to saidgenerating means only between the constant width pulses in the pulsetrain.
 15. Measuring apparatus, as defined in claim 13, and includingmeans operable while power to said analog signal generating means isinterrupted for maintaining said modulated pulse train at its amplitudeprior to the power interruption.
 16. A method for measuring the quantityof material transferred through a region, comprising the steps of: a.generating a train of constant width pulses having a frequencyproportional to the speed at which material is transferred through theregion; b. modulating the amplitude of the pulse train in proportion tothe instantaneous weight of material in the transfer region: and c.filtering the modulated pulse train to produce a continuous signalproportional to the product of the weight of material in the regiontimes the transfer speed, whereby the magnitude of the filtered signalis a measure of the instantaneous rate at which material is transferredthrough the region.
 17. A method for measuring the quantity of materialtransferred through a region, as set forth in claim 16, and furtherincluding the steps of: d. converting the filtered signal into a secondpulse train having a pulse rate proportional to the magnitude of thefiltered signal; and e. totalizing the pulses in such second pulse trainas a measure of the total quantity of material transferred.